Unrelated to RVMs, Igaki et al. “Real-time fingerprint sensor using a hologram” Applied Optics, Vol. 31, Issue 11, pp. 1794-1802 (1992) discloses a fingerprint sensor, wherein a beam is introduced into a prism from one of its slanted surfaces. This beam is arranged so as to meet the conditions for total internal reflection at the top surface of the prism. When a finger is placed on top of this surface, the conditions for total internal reflection are no longer met at the points of contact. Consequently light incident at these points will not be reflected and an image is created of the fingerprint. This image then passes out of the prism at the other slanted surface and is brought into focus on the image pickup element (charge-coupled device (CCD)) with the help of a lens system.
Also unrelated to RVMs, GB 1484613 discloses a windscreen soiling sensor comprises a light source emitting light through prism and windscreen so that it suffers total internal reflection from dirtiable surface, when it is clean, and, in the same housing, photometer sensing changes, due to windscreen soiling, of the light transmitted back through prism. The light is passed through focusing system and reflected from mirror and again focused by system, on to photometer, with iris, supplying a signal circuit which may, if the change exceeds a limit, switch on a windscreen cleaner.
Bonding has the same refractive index as the adjacent components.
Also unrelated to RVMs, GB1395113 discloses an apparatus for detecting obscuring matter, e.g. dirt, condensation, on a lamp glass or windscreen of a vehicle. The apparatus comprises means for directing a modulated optical or infrared beam on to the screen or glass and means for detecting correspondingly modulated radiation back-scattered from the screen by obscuring matter. A light-emitting diode, a photodetector and a control circuit are provided. A further embodiment utilizes the effective change in total internal reflection caused by back-scattering resulting from contamination. In this mode light is directed into the edge of the glass.